Retinal neurons express unique responses to neurotransmitters. Glutamate evokes hyperpolarizations as well as depolarizations. GABA responses are commonly antagonist-insensitive. The project goals are 1) to study responses of retinal neurons to exogenous pharmacological stimuli, as well as natural light stimuli, and 2) to understand the relationships between receptor expression on retinal neurons, the neural circuitry of retina, and retinal information-processing tasks. The study examines acutely dissociated retinal neurons from rat and zebrafish, and in-situ neurons identified in zebrafish retinal slices. Acutely dissociated bipolar and horizontal cells retain their shapes and can be morphologically identified in culture. Cells in retinal slices are identified morphologically by intracellular dye injection via the recording electrode. Physiological responses of isolated cells are assayed with voltage-sensitive probes; whole-cell patch clamp techniques are used to record the responses of neurons in the retinal slice. Dissemination of knowledge in retinal neurobiology through WEBVISION, an internet- based tutorial, continues to be a subsidiary goal of this project. Four glutamate-receptor types were identified on zebrafish bipolar-cell dendrites with whole-cell patch clamp recordings in retinal slice and localized puffs: 1. A conductance increase (Erev ~ 0mV) in presumed OFF bipolars. Such responses were kainate sensitive and CNQX blocked. 2. An APB-like conductance decrease (Erev ~ 0mV) in presumed ON bipolars. 3. A glutamate- gated chloride conductance increase in presumed ON bipolars. 4. A combination of mechanisms 2 and 3 in presumed ON bipolars. No bipolars responded to NMDA. One bipolar-cell axonal bouton always occurred in the ON or OFF inner-plexiform-layer sublamina appropriate to the presumptive response polarity, though many axons were multistratified with boutons in both sublaminae. These findings indicate a diversity of glutamate conductance mechanisms generate the light responses in zebrafish ON-, but not OFF-, bipolar cells, and that there likely is mixing of ON and OFF signal inputs in inner-plexiform-layer sublaminas a and b .